Page:Africa by Élisée Reclus, Volume 3.djvu/83

GEOLOGY OF THE CANAEIES. 67 guese prince from the fatal battlefield of Alkazar-el-Kebir, cherisli the tope tliat the undiscovered land will at the same time rise above the surface of the waters. Geology of the Canaries. The Canaries are not disposed in any regular order, although roughly forming the arc of a circle, whose convex side faces southwards. But Gomera and Hierro lie beyond this curve, and the archipelago consists rather of two distinct groups — Lanzarote, Fuerteventura, and neighbouring islets in the east ; the five other large islands in the west. The first group runs parallel with the continental seaboard ; the second, on the contrary, is disposed at right angles with the mainland. The two eastern islands stand on a common submarine plateau, whereas all the others lie in deep water, where in some places a thousand-fathom sounding line fails to touch the bottom. Lanzarote and Fuerteventura again are but slightly elevated compared with the western group, presenting in fact a steppe formation like that of the opposite continent. All, however, are alike of volcanic origin, their contour being nearly everywhere broken by headlands formed by eruptive rocks, while the primitive or sedimentary formations occupy a very small space amid the lava beds covering most of the surface. Their very aspect attests the antiquity of most of the trachytes, basalts, or obsidians in the western group, where the slopes of the hills are generally furrowed by deep gorges excavated in the course of ages by the running waters. Hence it is difficult to recognise the primitive form of the lava streams formerly ejected from the volcanoes, while in many places the craters themselves have disappeared. Gran Canaria (Great Canary), central member of the whole archipelago, where no eruption has occurred during the historic period, has been most weathered by atmospheric influences, by which the rocks have here been sculptured anew. Vast cirques have thus been opened for the rains of the interior, and the debris carried away seawards, the amount of denudation represenling a considerable part of the original insular mass. The absence of vapour jets and of thermal springs also bears witness to the antiquity of the volcanoes in the Canaries, compared with those of the Azores, which still abound in gases and boiling waters. No doubt there have been extensive discharges of lava and violent earthquakes even since the rediscovery of the archipelago; but these 'phenomena have been confined to the three islands of Lanzarote, Palma, and TenerifFe. Nor do the local records speak of ephemeral islands analogous to those heaps of scoriae which have so often appeared and disappeared in the Azorian waters. The only instance occurred during the series of eruptions which lasted for six years in the western district of Lanz.irote, when flames mingled with vapour flashed up close in-shore, and cones of scoriae, rising above the surface, gradually expanded until they became attached as headlands to the coast. On the same occasion the marine inlet of Janubio was converted into a lake by the enormous quantity of scoriae thrown up by the craters. 6S— AF